Abstract 4374: Identification of novel, biologically relevant, G-quadruplexes formed within the critical promoter of kRAS as promising molecular targets.

Abstract

Abstract To date, kRAS is one of, if not the, most established oncogenic anomalies identified. It is either upregulated or mutationally activated in a variety of cancers, most notably pancreatic adenocarcinoma, non-small cell lung and colon cancers. Pancreatic cancer carries the highest mortality rate of all cancers, with only a 3-6 month median survival, and a 5-year survival of <5%. Lung and colon cancers harboring a mutant kRAS are associated with a worsened prognosis and shorter disease-free survival, and such mutations are independent factors for poor prognosis. To date no attempts to modulate kRAS activity, localization, or signaling have produced clinically active moieties; there is a desperate need for new, kRAS-focused therapeutics. Various silencing technologies have demonstrated that decreasing kRAS expression is sufficient to produce cancer cell kill, and the presented works describe a novel target to downregulate kRAS expression - secondary structures within the proximal promoter, which contains a unique string of G-rich DNA. Negative superhelicity induced by transcription results in this region opening up to form unique secondary structures called G-quadruplexes (G4s). These G4s most often act as silencer elements, forming globular structures that mask binding sites for transcriptional factors, allowing for specific molecular targeting by small molecule drugs, modulating transcription, and protein expression. The G-rich region of the kRAS promoter is extensive, containing three separate putative G4-forming regions. Initial works described the near G4 as a unique ‘kinked’ structure, as well as described two compounds that stabilize different isoforms of this structure, but do not appear to contribute much to the transcriptional control of kRAS. Further elucidation of promoter activity has highlighted new, and more biologically important, G4s existing more distally from the transcriptional state site. Stabilization of this region in a plasmid system significantly decreases luciferase expression, and the mid-G4-forming region forms several stable, complex, structures. These formations have been examined by EMSA, polymerase stop, and footprinting methods. From these data, the elucidated predominant structures are currently the target of further studies with the ultimate goal of describing a new molecular structure, and its dynamic regulation, for future drug development. Citation Format: Chi-Fan Hockings, Kristen M. Greer, Tracy A. Brooks. Identification of novel, biologically relevant, G-quadruplexes formed within the critical promoter of kRAS as promising molecular targets. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4374. doi:10.1158/1538-7445.AM2013-4374